The Development of Cast Wheels

In motorcycle racing, horsepower, handling and tire performance have always been inextricably linked. And in the early '70s great leaps of performance were made in all these areas and this carried on into the '80s. Traditional twin-loop steel frames gave way to aluminum-spar chassis, power went over and above 100, then 120 and 140 horsepower, tires became slicks, slicks became Radials and so on.

One important part of the package, which had to work with all these changes and was crucial to them all, was the introduction of the cast wheel, during the '70s.

In 1975 Giacomo Agostini's title-winning Yamaha OW-23 featured cast wheels by the end of that season. With power heading upwards courtesy of the arrival of the two-strokes, wheel and tire design had to keep up. The 'traditional' spoked or laced wheel looked great, but like a biplane criss-crossed with rigging wires, it was fast becoming an anachronism.

In general terms spoked wheels needed attention on road and race motorcycle. You needed to check how tight the spokes were often, you had to keep them clean and free from rust and you had to run an inner tube. Cast wheels were tougher, maintenance free and became a fashion all of their own. In motorcycle racing circles aluminum soon gave way to magnesium as the material of choice, with the likes of Marvic producing their first three-spoke magnesium wheel in 1983 for Grand Prix racing use.Magnesium wheels weighed less, which meant less unspung weight. Less unsprung weight meant the suspension didn't work as hard and lighter wheels meant quicker turning, and in turn this reduced overall weight, meaning tires and brakes could be lighter too.

Once more racing was driving motorcycle technology forward, and the advantages of the cast wheel were soon finding favor on road going motorcycles.

Laverda's Jota of 1975 had cast wheels made by the Italians themselves, while by 1978 the likes of Kawasaki's Z1-R was sporting cast wheels and the big Kawasaki Z1 never really looked back. It was the same across the board, with cast wheels soon becoming the wheels of choice, not that they weren't without their own problems.

You see, while they may have been 'zero-maintenance' compared to spoked wheels, the truth was more prosaic. Early cast alloy wheels on both two and four wheels sometimes had a problem with leaking.

Many blamed poor casting of the wheels where, literally, the metal was porous and air would leak out. Some wheels were better than others. On some the leakage was more accurate for measuring time than an atomic clock. Some fixed the issue by running tubes in tubeless tires, but obviously as the years went on things improved. New materials and new methods of making wheels came along. So that by the time we were running our extruded-rim ComStars on our Honda CB400 SuperDreams things weren't quite so bad, even if the motorcycles were.

In more modern times the lightweight wheels became a performance upgrade, with Dymags and Marvics being used to replace the heavier, stock items. In general the 'feeling' you get on lightweight wheels can be very different to standard, heavier ones – but obviously a lot depends on what other parts have been changed. So, as well as the feel changed. So, as well as the feel of quicker turning, feedback through the suspension is improved and there's more of a 'connection' with the Tarmac.

The development of the modern cast wheel hasn't been without problems.

Despite being very strong, some magnesium and alloy wheels have been known to crack – sometimes with disastrous consequences. Take Robert Dunlop's horrifying crash at the 1994 Isle of Man TT. His rear magnesium Marvic single-sided wheel on his RC45 shattered just after landing the jump at Ballaugh Bridge. Dunlop was thrown head first into a wall and suffered career-threatening leg and arm injuries. At the time other magnesium wheels were checked and some were found to have cracks. Some racers would send their wheels off to be X-rayed once a year but many felt that perhaps wheels were getting a little too light for the stresses of road-racing and that perhaps it was best not to use them on the road. Even standard wheels have buckled...

Of course in off-road or on adventure motorcycles the cast wheel has never dominated. Things is, cast wheels are more likely to crack or snap rather than bend when hitting a tree stump. And they're not easy to fix when you're kilometers from the nearest garage, let along the nearest foundry.